January 16, 2013
NASA first dipped its toe into climate-change research in the 1980s by using satellite and aircraft imaging. Its efforts grew more serious with the launch of a large network of satellites in 1991. And by 2004, the agency was spending $1.3 billion annually on climate science. It now has more than a dozen spacecraft studying everything from the oceans to the atmosphere to the cryosphere (the Earth’s frozen bits). On Friday, it will add the stratosphere to that list when it launches an unmanned Global Hawk aircraft from California’s Edwards Airforce Base.
The project, called Airborne Tropical TRopopause EXperiment (ATTREX), will study humidity in the tropical tropopause layer, the area of the atmosphere eight to 11 miles above the Earth’s surface that controls the composition of the stratosphere. According to ATTREX scientists, small changes in stratospheric humidity can significantly affect climate. “Cloud formation in the tropical tropopause layer sets the humidity of air entering the stratosphere,” principal investigator Eric Jensen says, adding that the pathways through the tropical tropopause influence the chemical composition of the stratosphere.
Although the group won’t focus on the impact of standard greenhouse gases such as carbon dioxide and methane, water vapor is a powerful greenhouse gas, and understanding its variability within the stratosphere is the group’s priority. Filling in this gap, they believe, will allow scientists to forecast how changes in the stratosphere affect global climate change, which will in turn improve the accuracy of mathematical models used in climate change predictions.
The tropopause and stratosphere have proven elusive to climatologists until now. “We’ve been wanting to sample this part of the atmosphere for a long time,” Jensen says. The problem has been access — a specialized high altitude aircraft is necessary to conduct this type of research.
Enter the Global Hawk, which can travel up to 65,000 feet into the atmosphere for up to 31 hours at a time and is fitted with instruments that can measure surrounding temperatures, clouds, trace gases, water vapor, radiation fields and meteorological conditions. All of this will let the ATTREX team sample a range of conditions over a large geographic span. Test flights conducted in 2011 showed that the Global Hawk and its instruments can withstand the frigid (as low as minus-115 degree Fahrenheit) temperatures above the tropics.
They’ll send the craft above the Pacific Ocean near the equator and off the coast of Central America six times over the course of the next two months, monitoring it from the ground while it’s in flight. “We get high-speed real-time data back from the aircraft via satellite communications,” Jensen says. “The instrument investigators monitor and adjust their instruments, and we use the real-time data to adjust the flight plan throughout the flight.”
ATTREX is one of the first projects launched by NASA’s new Earth Ventures program, which provides five years’ funding to low- to moderate-cost missions. This is far more time than previous airborne-science studies, and the ATTREX crew will use the added time to re-launch the Global Hawk in winter and summer 2014, allowing them to look at seasonal variation.
The longer timeframe is also conducive to international collaborations. In 2014, the ATTREX team will venture to Guam and northeastern Australia. In Guam, they’ll connect with British researchers, who will be using a low-altitude aircraft to study climate change, and a National Science Foundation crew doing similar research with a G5. “We’ll have measurements from the surface all the way to the stratosphere,” Jensen says. “And we’ll be able to connect emissions at ground level up to measurements of the composition in the stratosphere.”
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